Photographic antihalation and protective layer comprising a nitrated styrene-maleic acid copolymer



' 2,984,568 PHOTOGRAPHIC TIVE LAYER COMPRISING A NITRATED STY-RENE-MALEIC ACID COPOLYMER Ren Maurice Hart, Wilrijk-Antwerp, andLaurent Pierre Roosens and Jacques Ren Troquet, Antwerp, Belgium,assignors to Gevaert Photo-Producten N.V., Antwerp, Belgium, a Belgiancompany No Drawing. Filed Nov. 26, 1957, Ser. No. 698,902

Claims priority, application Belgium Nov. 26, 1956 7 Claims. (Cl. 96-84)The present invention relates to a photographic element provided with analkali soluble hydrophobic outer layer containing as the mainconstituent a layer-forming polymer, and more particularly to aphotographic element provided with an antihalation backing or with aprotective layer applied to the light-sensitive silver halide layer orto the layer bearing already a silver image or a color image.

It is known to provide photographic elementssuch as black-and-whitefilms and multilayer color films with an antihalation backing in orderto inhibit light reflec tion from the back side to the emulsion side.This layer generally consists of a binding agent such as gelatin or asynthetic polymer, and a substance absorbing the light rays of thisregion of the spectrum to which the silver halide emulsion (or, in thecase of a multilayer film, the emulsion layernearest to the support) issensitive.

It is further known to apply a protective layer (e.g. an anti-abrasivelayer or a layer which absorbs the ultraviolet radiations) consisting ofa layer-forming polymer to the light-sensitive layer (no the sensitivelayers) or to a layer bearing already a silver image or a color image.

The polymeric products which are to be used as binding agents in outerlayers such as the above-mentioned antihalation or protective layersmust meet several severe requirements. Besides the particular functionof these layers, they must in any case, on account of their position,possess special mechanical properties and show a resistance to outerinfluences such as friction, pression, water, moist air etc. so that thefilms, plates or photographic papers provided with such layers can betreated in the processing baths and/or in the apparatus, e.g. cameras orprojection apparatus, without being damaged.

If these layers must be applied to a flexible support, the layer-formingpolymers must moreover be chosen in such a way that the formed layerspossess a sufiicient flexibility. Another requirement which particularlyconcerns the antihalation layers consists therein that neither thislayernor a constituent thereof may be transferred onto the silver halideemulsionlayer if the emulsion layer and the backing layer come intocontact e.g. when a photographic film is wound.

If it is desired that the layers are to be removed during the treatmentin the usual photographic baths (e.g. in the case of antihalation layerscontaining a light-absorbing substance which is not or not completelydecolorized in the processing baths), the polymeric binding agent mustmoreover be sufiiciently soluble in the developers, which frequentlyareonly slightly alkaline. On the other hand, the sensitivity to the alkalimust not be too high since the contact of these layers e.g. with wethands would damage the photographic element. A further requirement isthat the layers obtained from the polymeric binding agent must be becomesticky in moist atmosphere. a t The derivatives of the styrene-maleicacid copolymers AN TIHALATION AND PROTEG erties. In moist atmospherethese layers become smooth provide new and improved antihalationcoatings and which hitherto have been proposed as binding agent forantihalation layers do not possess the required propand sticky, whichinvolves a transfer of the colored particles of the antihalation layeronto the emulsion layer on winding and on storing the photographicelement.

It is therefore an object of the present invention to protective layers.Another object is to provide such layers the flexibility of which isperfectly adapted to that of the usual flexible photographic supports towhich they are to be applied. Another object of the invention is toprovide antihalation coatings and protective layers which possessoutstanding mechanical properties, such as an exceptional resistance toscratching and improved gliding properties. A further object is toprovide such antihalation coatings which can be removed readily byweakly alkaline solutions such as the usual photographic developers. Astill further object of our invention is to provide antihalationcoatings and protective layers with hydrophobic character which possessexceptional resistance to moisture.

The above objects are accomplished in accordance with the presentinvention when the antihalation coating or the protective layer containsas the main constituent a nitrated styrene-maleic acid copolymer.

In order to obtain antihalation layers according to the presentinvention, an organic dyestuff or a mixture of such dyestufis dissolvedin an appropriated solvent can be incorporated in a solution of anitrated styrene-maleic acid copolymer. Suitable antihalationdyestufiscan be found e.g. among the styryl dyestuffs, the triand di-aryl methanedyestuffs and the azomethine dyestuffs. The antihalation layer can beapplied to a usual support such as e.g. to a flexible light-transmittingfilm support or to a glass plate, which is to be provided on the otherside with a light-sensitive silver halide emulsion layer.

According to another embodiment of the present in vention, antihalationlayers can be prepared by starting from pigment dispersions e.g. carbonblack in the polymeric binding agent. In this respect the nitratedstyrenemaleic acid copolymers possess the great advantage to give stabledispersions by simply mixing, whilst stirring, the pigment with asolution of the polymer in an organic solvent such as a lower alcohol,without any addition of a dispersing agent. It is to be noted that theprepara tion of such dispersions with the polymers as used hither to forthe same purposes always necessitates an intense" mechanical treatment,e.g. in a colloid mill. The black dispersion can be applied asantihalation coating toa suitable support as described hereinbefore.

When the nitrated, styrene-maleic acid copolymers are i to be applied asa protective layer on a light-sensitive emulsion layer or on aphotographic image-bearing layer, especially a color image-bearinglayer, ultra-violet radiation absorbing substances, such asdiaminostilbene derivatives, derivatives of coumarone, pyrazoline orimidazoline, may be incorporated in the solution of the polymer. Thesupport for the emulsion layer or for the image bearing layer can bee.g. a flexible film or a barytacoated paper.

The nitrated styrene-maleic acid copolymers are ob tained by action ofnitric acid upon styrene-maleic acid copolymers. Although in generalfuming nitric acid hitherto was used therefor, a great part (up to 70%)of the fuming'nitric acid can be replaced by ordinary nitric acid. Inthe circumstances the reaction runs very smoothly at room temperature.Also a mixture of nitric acid and sulphuric acid can be used. In theevent, the reaction is better carried out whilst heating e.g. between 50and 70 C. Also the proportion nitric acid/ sulphuric acid is ofimportance and the best resultsare:

estates;

attained with proportions ranging from 7/3 to 9/1. In this way about onenitrogrou'p per styrene unit is incorporated. which-theoreticallycorresponds with a nitrogen content'of5.3%. 9

- The degree of polymerization of the starting products is only slightlyinfluenced by the nitration. This degree of polymerization is not ofparticular importance in the preparation of ordinary antihalation layerswith soluble dyestuffs; but must be taken into account in thepreparation of antihalation backings containing carbon black. In thiscase, polymers with a relatively low molecular weight are preferablyused so that strongly concentrated solutions (25 to 35%) can be preparedwhich do not show an excessive viscosity. 4

' Hereinafter follow some examples of preparing the nitratedstyrene-maleic acid copolymers. W

PREPARATION l (a Styrene-maleic, acid copolymer i 41.6 parts by weightof styrene (previously washed with a solution of sodium hydroxide andwater. respectively; dried upon calcium chloride and distilled innitrogen atmosphere under reduced pressure) are copolyme'rized with 43.1parts by weight of maleic acid anhydride' in 730 parts by volume oftoluene, previously dried upon calcium chloride. The mixture is heatedat'1l0 C. for 9 hours in the presence of 0.42 part by weight ofazobisisobutyronitrile as initiator. The polymerization mixture isfiltered and the deposited styrenemaleic acid copolymer is'washed withhexane and dried in a desiccator at '50? 'C.

(b) Nitrated .rt yrene-m aleic acid copolymer 80 parts by weight of astyrene-maleic acid copolymer are dissolved whilst stirring in 400 partsby volume of fuming nitric acid, whilst the temperature is kept below C.by ice-cooling. V

The clear solution is precipitated in distilled water. The precipitateis pulveriied and washed with distilled water to neutral reaction as canbe controlled with indicator paper. The product is dried under vacuum at40, C. It contains 5.6% of nitrogen.

PREPARATION 2 3 50 crnfi of strong nitric acid (d=1.42) and'l50 cm. offuming nitric acid (ab- 152) are brought into a reac-. tion flask, and100 g. of'styrene-maleic acid copolymer are gradually added whilststirring at a temperature kept between 2 5 and 30 C. After standingovernight the solution is added to water and the formed precipitate iswashed with water.

The product is dried under vacuum to constant weight. It contains 5.4%of nitrogen.

PREPARATION 3 A nitrated styrene-maleic acid copolyrner is prepared byvcausing 1 kg. of the styrene-maleic acid copolymer to react withv 6.3liter of strong nitric'acid (d l.42) and 9.95 liter of sulphuric acid(96%) for 8 hours at 60 C.

The formed reaction product is separated in the same way. as in theprevious examples. It contains 5.5% of nitrogen. a V

The following examples illustrate the invention without limiting,however, the scope thereof.

- A EXAMPLE 1 A solution of 60 g. of a nitrated styrene-maleic acidcopolymer in amixture of 300 crn. of ethanol and 300 c COf methal'l01 isprepared. This solution (hereinafter called A) is added to a solution of22 g. of a green dyestufi (known under the denomination Bro 721 anddescribed. in' BIOS comp. 146/2/ 382/ 30), in a mixture 015-209 cmfii ofethanol and200cm. of methanol (solution B). This solution; is coated onthe rear of a cellulose aceto-butyrate' film support, the front sideof.which is to. be provided with a panchromatic sensitized silveriodoare dissolved in a mixture of 200 cm. of ethanol and ns baths-ExaMPLE 2' 22 g. of a dyestufi of the following formula (IJH2-CH2QH aredissolved in a mixture of 200 cm. of ethanol and 200 cm. of methanol.This colored solution is added to solution A described in Example 1.After application to the rear of a cellulose triacetate film supportwhich'is to be provided with an orthochromatic sensitized silverchloro-bromide emulsion, a deep-red colored layer is ob 200 cm. ofmethanol. This solution is added to the solution A described inExample 1. After application to a suitable support in the mannerdescribed in Example 2 an orange-colored layer is obtained whichdecoloriz es in the processing baths.

EXAMPLE 4 22 g. of. a dyestuff described in PB report 74174, frame 820.(US. Government, Office of Technical Services, Washington), aredissolved together with 60 g. of nitrated styrene-maleic acid copolymerin a mixture of 500. cm. of ethanol and 500 cm. of methanol. After ap;plication to a flexible support which is to be provided with three,differentially sensitized silver halide emulsion layers contining colorcouplers, a violet layer is obtained. This layer d'ecolorizes anddissolves in the photographic processing baths. 7

- EXAMPLES 7 g. of carbon black are added to a solution of 60 g.ofanitratedstyrene-maleic acid copolymer in 250 cm.3 of ethanol, whilstthoroughly stirring. After dispersing the carbon black, the volume is.brought to 1 liter by adding a mixture of 1 part of ethanol and 2 partsof methanol.. This solution can be cast onto a flexible support; Abrown-black layer is obtained which is eas removable in photographicprocessing baths. The

layer, a photographic element eg a positive motion pic: ture color film,provided therewith, is free from halae tion. V V

. EXAMPLE 6 A solution of 9 g. of a nitrated styrene-maleic acidcopolymerv in a mixture. of 700 cm. of ethanol and B QQ cm. -of m thanolis coated as an anti-abrasive layer onto a silver chloro-bjromideemulsion layer on a baryta-coated paper support. The photographicproperties of the tlight sensitive lays .11 2 99;matlfidl she-na cremais- 9 friction fog is periods of stockage, and moreover thelight-reflection being almost completely. inhibited by considerablydiminished in respect of those of a photographic emulsion withoutprotective layer.

EXAMPLE 7 75 g. of a nitrated styrene-maleic acid copolymer and 5 g. ofTeregitol NP 35 (trademark for alkylphenylpolyethylene glycol ether) aredissolved in a mixture of 600 cm. of ethanol, 160 cm. of ether, 100 cm.of isopropylalcohol and 50 cm. of methylene-glycol. This solution ismechanically applied to the image-bearing layer of an exposed anddeveloped motion picture film of the positive type. This layer protectsthe film against scratching, moisture and mishandling during thetreatment.

EXAMPLE 8 12 g. of Uvinul 400 (a substituted benzophenone) are added thesolution of the copolymer described in Example 6. This solution isapplied as protective layer on the emulsion layer of a photographicnegative film. This layer protects the emulsion against ultra-violetrays.

We claim:

1. A photographic element comprising a support, at least onelight-sensitive silver halide emulsion layer, and an alkali-solublehydrophobic outer layer, said outer layer being mainly constituted by anitrated copolymer consisting of 50 mol percent styrene monomeric unitsalternating with 50 mol percent maleic acid monomeric units, thecopolymer containing 0.8 to 1.2 nitro groups per styrene monomeric unit.

2. A photographic element comprising a flexible lighttransmittingsupport, at least one light-sensitive silver halide emulsion layer onone side of said support, and an alkali-soluble hydrophobicanti-halation layer on the other side of said support, saidanti-halation layer comprising a copolymer and a light-absorbingsubstance, said copolymer consisting of 50 mol percent styrene monomen'cunits alternating with 50 mol percent maleic acid monomeric units, thecopolymer containing 0.8 to 1.2 nitro groups per styrene monomeric unit.

3. The photographic element according to claim 2, wherein thelight-absorbing substance is an organic dyestuff.

4. The photographic element according to claim 2, wherein thelight-absorbing substance is carbon black.

5. A photographic element comprising a support, at least onelight-sensitive silver halide emulsion layer on one side of saidsupport, and an alkali-soluble hydrophobic protective layer coated onsaid emulsion layer, said protective layer being mainly constituted by acopolymer consisting of mol percent styrene monomeric units alternatingwith 50 mol percent maleic acid monomeric units, the copolymercontaining 0.8 to 1.2 nitro groups per styrene monomeric unit.

6. The photographic element according to claim 5, wherein the protectivelayer includes an ultro-violet radiation absorbing substance.

7. A photographic element comprising a support, at least oneimage-bearing layer, said image having been obtained by exposing tolight a light-sensitive silver halide emulsion layer on one side of saidsupport, said element further ocmprising a. protective layer coated onsaid image-bearing layer, said protective layer being mainly constitutedby a copolymer consisting of 50 mol percent styrene monomeric unitsalternating with 50 mol percent maleic acid monomeric units, thecopolymer containing 0.8 to 1.2 nitro groups per styrene monomeric unit.

References Cited in the file of this patent UNITED STATES PATENTS2,077,789 Hagedorn Apr. 20, 1937 2,173,480 Jung Sept. 19, 1939 2,274,551Kenyon et al. Feb. 24, 1942 2,685,512 Sawdey Aug. 3, 1954 2,748,029Spear et al. May 29, 1956 FOREIGN PATENTS 115,781 Australia Aug. 25,1942 UNITED STATES} PATENT OFFICE CERTIFICATE OF CORRECTION Patent N0.2,984,568 May 16, 1961 Ren Maurice Hart et a1.

It is hereby certified that error apfaears in the above numbered patentrequiring correction and that the said Letters Patent. should read as"corrected below.

Column 1, line 35, for "no" read or same column, line 70, for "be" readnot Signed and sealed this 21st day of November 1961.

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of PatentsUSCOM M-DC-

1. A PHOTOGRAPHIC ELEMENT COMPRISING A SUPPORT, AT LEAST ONELIGHT-SENSITIVE SILVER HALIDE EMULSION LAYER, AND AN ALKALI-SOLUBLEHYDROPHOBIC OUTER LAYER, SAID OUTER LAYER BEING MAINLY CONSTITUTED BY ANITRATED COPOLYMER CONSISTING OF 50 MOL PERCENT STYRENE MONOMERIC UNITSALTERNATING WITH 50 MOL PERCENT MALEIC ACID MONOMERIC UNITS, THECOPOLYMER CONTAINING 0.8 TO 1.2 NITRO GROUPS PER STYRENE MONOMERIC UNIT.